In conventional motor driven cameras, the camera is required to perform multiple mechanical operations. The camera's operations include, for example, winding and rewinding the photographic film, driving the camera's mirror and shutter, and, in autofocus cameras, driving the lens focal length. Generally, providing separate drive capability for mechanical operations performed by a photographic system increases the complexity and cost of the equipment undesirably. Thus, it is desirable to use a single drive motor to drive one or more of the camera's mechanical operations.
U.S. Pat. No. 4,162,837 by Haragushi, assigned to Ashai Kogaku Kogyo Kabushiki Kaisha, issued Jul. 31, 1979, discloses a motor drive device for a camera for winding and rewinding the film and driving the camera's shutter. U.S. Pat. No. 5,025,277 by Inoue, assigned to Olympus Optical Co., Ltd., issued Jun. 18, 1991, discloses a camera which includes a motor and gear mechanism for winding and rewinding the film and switching the focal length of a photographic lens. U.S. Pat. No. 5,105,212 by Kitazawa, assigned to Ashai Kogaku Kogyo Kabushiki Kaisha, issued Apr. 14, 1992, discloses a motor driven camera for winding and rewinding the film and driving the shutter and the diaphragm.
The drive motor mechanisms disclosed in the above described references are not applicable to cameras using thrust film cartridges. Thrust film cartridges utilize film door light traps as an alternative to conventional film cartridges utilizing plush light traps. Typical thrust film cartridges include an outer shell having a longitudinally-extending opening allowing for the exit of film from the cartridge. A cartridge spool is rotatably positioned within the outer shell to accommodate a roll of film. A film door is rotatably mounted adjacent the opening and is movable between a closed position, wherein a light tight seal is formed, and an open position, wherein film is allowed to exit the cartridge.
Thrust film cartridges are particularly useful for allowing rewinding, removal and subsequent reloading of the film cartridge before the complete roll of film is used. Cameras which allow for the rewinding, removal and reloading of partially-used rolls of film are sometimes referred to as mid-roll interrupt cameras. Such a camera is disclosed in commonly-assigned U.S. Pat. Nos. 4,947,197 to Smart et al. and 4,965,600 to Smart et al., which are incorporated in their entirety herein by reference.
In order to ready the film within the camera for exposure, the film door of the thrust film cartridge must first be opened. Further, in order to ready the film cartridge for return to the camera user, the film door of the thrust cartridge must be closed after the film has been completely rewound into the film cartridge. Thus, it would be desirable to provide a differential gear mechanism, which, in addition to advancing and rewind the film, also operates to open and close the film cartridge door.
It would be desirable to provide a method of selectively constraining and/or releasing portions of a differential gear mechanism to direct a motor's drive power to the operations of opening the film cartridge door, advancing the film, rewinding the film and closing the film cartridge door. It would be desirable to provide purely mechanical operation to open and close the film cartridge door to avoid the need for electromechanical devices to ensure the door is fully open or fully closed. It would be desirable to provide a mechanical operation, as opposed to an electromechanical operation, to detect whether the film has been completely rewound in the film cartridge before initiating the operation of closing the film cartridge door. It would be desirable to provide a purely mechanical film door release option which can be activated only after film cartridge door is closed.